Apparatus and methods for selective thermoforming

ABSTRACT

Apparatus and methods of forming selected portions of integral sheets of material are disclosed. Unformed portions of the sheets may remain undistorted during the forming process, allowing them to contain text, art work, or other desired information without material risk of the information being degraded or becoming unintelligible during the forming process. This result may be accomplished, moreover, with less trim than usually occurs in conventional forming processes.

REFERENCE TO PROVISIONAL APPLICATION

This application is based on, claims priority to, and hereby refers toU.S. Provisional Patent Application Ser. No. 61/350,107, filed Jun. 1,2010, the entire contents of which are incorporated herein by thisreference.

FIELD OF THE INVENTION

This invention relates to shaping heated polymeric materials in a moldand more particularly, although not necessarily exclusively, to heatingselected areas of the materials to forming temperatures while notforming other areas of the materials.

BACKGROUND OF THE INVENTION

Conventional thermoforming involves heating a polymer sheet to a pliableforming temperature (which depends at least in part on the type of sheetbeing heated), forming the sheet to a specific shape on a mold, andthereafter trimming unformed portions of the sheet to create a usefulproduct. The sheet, sometimes referred to as “film” when thin gauges orcertain types of materials are formed, is typically heated in an oven tothe forming temperature so that it may be stretched into or onto a moldand then cooled to retain a finished shape. During the heating process,the entire sheet of material is heated to the forming temperature.Portions of the sheet that are not formed are usually referred to as“trim” and not reused until after further processing.

U.S. Pat. No. 4,878,826 to Wendt, the entire contents of which areincorporated herein by this reference, is one of many patents disclosingapparatus for thermoforming articles from sheets of plastic material.The apparatus of the Wendt patent may include both male and female moldstogether with a heating means and evacuation equipment. One such heatingmeans is described as being hot oil circulating through an associatedmanifold such that it crystallizes a sheet of plastic material. SeeWendt, col. 10, 11. 9-12. According to the Wendt patent, the sheet alsomay be pre-heated to 10-15% crystallization before entering the mold.See id., col. 12, 11. 50-57. Indeed, over-crystallization of the sheetapparently is an issue with the apparatus of the Wendt patent, requiringcold air to be injected into various mold cavities. See id., col. 13,11. 53-65.

Thermoforming a plastic sheet necessarily distorts it. However, in somecircumstances distortion of certain portions of a sheet is undesirable.As an example, distortion of portions of a sheet containing printing orart work may render them unintelligible or, at minimum, diminish theiraesthetic appeal. Consequently, conventional thermoforming requirespre-printing of text and art in a distorted form so that the furtherdistortion caused by the thermoforming can counteract the pre-distortionand, at least theoretically, produce intelligible images. Thus,providing apparatus and methods that would allow thermoforming ofselected portions of a plastic sheet while avoiding distortion of otherportions of the sheet thus would be a beneficial-albeitdifficult-achievement.

SUMMARY OF THE INVENTION

The present invention accomplishes this desired result. Notwithstandingits use of an integral sheet of polymeric material, the presentinvention allows heating and forming of only selected portions of thematerial. By contrast, unformed portions of the material remainsubstantially undistorted and thus may contain undistorted printing, artwork, or other text, symbols, or information without concern as towhether intelligibility of the information will be degraded during theforming process. Even if information is not present in unformed regionsof a sheet, the mere fact that the unformed regions may retain theiroriginal shapes (typically but not necessarily flat) and thicknessespermits a broader range of products to be created. Further, apparatusand methods of the present invention admit productive use of the vastmajority of each sheet (e.g. 95% in some cases), so that little trim iscreated when products are formed.

In at least some embodiments of the invention, energy-absorbing or-reflecting material may be employed to limit heat or other energytransferred to the polymer sheets. Such material may be in the form ofmetallic or other plates having simple or complex shapes. The plates mayinclude cut-outs so that heat or other energy may be transferredefficiently to areas of a sheet that is to be thermoformed. Variousembodiments of the invention also may utilize controllable banks ofheaters to allow variable heating of the molds themselves.

It thus is an optional, non-exclusive object of the present invention toprovide apparatus and methods for selectively thermoforming integralpolymeric materials.

It is another optional, non-exclusive object of the present invention toprovide apparatus and methods for thermoforming portions of a polymersheet while not forming, or otherwise materially distorting, otherportions of the sheet.

It is an additional optional, non-exclusive object of the presentinvention to provide apparatus and methods permitting text, art work, orother information to be printed on to-be-formed material in anundistorted manner yet remain intelligible post-forming.

It is also an optional, non-exclusive object of the present invention toprovide apparatus and methods for selective thermoforming including useof mechanical heat-transfer barriers.

It is yet another optional, non-exclusive object of the presentinvention to provide apparatus and methods in which the heat-transferbarriers are in the form of plates having cut-outs through which heatmay readily pass.

It is a further optional, non-exclusive object of the present inventionto provide apparatus and methods for selective thermoforming usingcontrollable banks of heaters to allow variable heating of the moldsthemselves.

It is, moreover, an optional, non-exclusive object of the presentinvention to provide apparatus and methods for selective thermoformingwhile limiting the amount of trim.

Other objects, features, and advantages of the invention will beapparent to persons skilled in the relevant art with reference to theremaining text and the drawings of this application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of exemplary thermoforming apparatus usefulas part of or in connection with the present invention.

FIG. 2 is a perspective view of a portion of a mold comprising part ofthe apparatus of FIG. 1.

FIG. 3 is a close-up view of part of the mold portion of FIG. 2illustrating especially various plugs protruding upward from its surfaceonto which a formable sheet may be placed.

FIG. 4 is a generally elevational view of an exemplary heat-sinkingplate that may comprise part of the present invention.

FIG. 5 is a close-up view illustrating a formed polymer sheet contactingthe mold part of FIG. 3.

FIG. 6 is a generally elevational view of an exemplary productthermoformed in the manner of the present invention.

FIG. 7 is a generally side (edge) view of an exemplary product similarto that shown in FIG. 6.

FIGS. 8A-C are various views of a plug consistent with FIG. 3.

DETAILED DESCRIPTION

Depicted in FIG. 1 is exemplary thermoforming apparatus 10. Apparatus 10may be a conventional thermoforming machine, any number of which areavailable commercially. Preferably included as part of apparatus 10 aremold 14 (see also FIGS. 2-3) and heater 18. A computerized controllerincluding actuating means 22 may, if desired, be connected to heater 18to control aspects of its operation. Actuating means 22 may comprise oneor more manual switches as shown in FIG. 1. Those skilled in relevantfields will recognize, however, that other manners of actuating heater18 may be employed instead and that no controller is required.

Heater 18 preferably is positionable above mold 14 so as to supply heatonly to one side of the mold 14, which itself may be heated. FIGS. 2-3show aspects of an exemplary version of mold 14, which preferably(although not necessarily) is made of aluminum. Alternatively, mold 14may be of composite type with both male and female components. Asillustrated particularly in FIG. 3, mold 14 may comprise a generallyplanar upper surface 26 from which one or more plugs 30 protrude. In useof apparatus 10, plugs 30 function as three-dimensional objects aboutwhich sheets of polymer material are formed.

FIGS. 8A-C illustrate aspects of an exemplary plug 30. Plug 30 may, ifdesired, be shaped generally as a cylinder and include section 31comprising upper surface 32 together with side 33. Formed in side 33 maybe one or more notches 35. At least two, and preferably three (or more)such notches 35 are incorporated into side 33, with the notches 35preferably (although not necessarily) being angularly spaced evenlyabout the circumference of plug 30. For example, if plug 30 includesthree notches 35, each notch 35 may be spaced one hundred twenty degrees(120°) from adjacent notches 35. As depicted in the side view of FIG.8B, notches 35 need not extend completely to upper surface 32—althoughthey may do so if desired.

Also detailed in FIGS. 2-3 as part of mold 14 are clamps 34 andalignment pins 38. Clamps 34 surround some or all of perimeter 42 ofmold 14 and retain to-be-formed material in place relative to uppersurface 26. Pins 38, which like plugs 30 extend upward from uppersurface 26, facilitate alignment of the to-be-formed material relativeto the plugs 30.

An exemplary heat sink 46 appears in FIG. 4. Sink 46 may be sized andshaped in any appropriate manner and may of any suitable heat-absorbing(or -reflecting) material. Preferably, however, sink 46 conforms to theshape of the corresponding mold or surface to be heated; as shown inFIG. 4, exemplary sink 14 is in the form of a generally rectangular,generally planar aluminum plate. Consistent with the present invention,sink 46 may include one or more cut-outs 50 through its depth, each ofwhich preferably is approximately the size and shape of an associatedplug 30. Sink 46 additionally may include openings 54 for receivingalignment pins 38.

Apparatus 10 may be utilized with any thermoformable material. Forcertain purposes identified herein, however, the material beneficiallyis polyethylene terephthalate (“PET”), a polymeric plastic resin.Additionally beneficial for various of these purposes is that the PET betransparent. Again, though, the thermoformable material need notnecessarily be clear or transparent, nor need it be PET. For ease ofhandling, the material advantageously may be preformed into a generallyplanar sheet of predetermined size and shape.

Among products usefully created using the present inventive techniquesare plastic display holders for coins or souvenirs. Collector-qualityversions of such holders may, and indeed typically, include colorprinting, art work, and text in unformed regions. By contrast, formedregions--into which coins are placed-preferably remain clear so as notto impede viewing of the coins. In some cases the holders may becombined back-to-back or placed within clear housings for furtherprotection of the coins. Objects other than coins or souvenirs may bedisplayed, and products other than display holders may be created,however, as should be apparent to persons skilled in the art.

According to at least one method of the present invention, mold 14 maybe heated to a preset temperature. The temperature may be selected so asto allow thermoformable material to be formed by the mold 14 and so asto be sufficient to remove heat from the material. Preferably, however,the selected temperature is such that warping or chill marks will not beformed on or in the material.

After mold 14 is heated adequately, a sheet of material containingundistorted color printing, art work, or text (or combinations thereof)may be laid onto upper surface 26 of mold 14. For at least some displayholders, up to six colors may be printed on each side of the sheet, withopaque material (text and art work) then printed over the printedcolors. Of course, any or all of the printed matter may be omitted ifnot needed in the final product. Nevertheless, when present, the printedmatter need not be pre-distorted, as it is not subject to materialdistortion during the forming process.

Assuming the above-described coin display holders are to be created, thesheet preferably contains openings through its depth for receivingalignment pins 38, with the openings themselves positioned so that, whenpins 38 are received, unprinted (clear) areas of the sheet arepositioned on upper surface 26 atop some or all of plugs 30. Clamps 34may then be employed to secure the periphery of the sheet against uppersurface 26. Thereafter, sink 46 may be placed atop the sheet, with itsopenings 54 likewise receiving alignment pins 38 and at least some ofits cut-outs 50 aligned with clear areas of the sheet. So placing sink46 effectively sandwiches the sheet between mold 14 and sink 46,precluding its longitudinal and lateral movement.

Following placement of the sheet relative to mold 14, heater 18 isrepositioned closely above sink 46 and activated for a selected periodof time. Continuing with the display holder example, heater 18 may beactivated for approximately thirty seconds. Heat or other energy fromheater 18 transfers to sink 46 and, where cut-outs 50 in sink 46 exist,to (clear) areas of the sheet therewith aligned, where it is absorbed bythe polymeric material.

As the exposed areas of the sheet absorb sufficient heat to reach theirforming temperatures, mold 14 is evacuated so as to stretch (form) thematerial around plugs 30. Heater 18 then may be repositioned away frommold 14, the formed sheet of material may be allowed to cool, and sink46 may be removed so as to expose the sheet of material. FIG. 5illustrates material 58 in this exposed state, with the material 58including (in this example) both unformed portions 62 and formedportions 66. The sheet of material 58 thereafter may be removed frommold 14 and, if appropriate, divided into display holders, examples ofwhich (designated 70A and 70B) are depicted in FIGS. 6-7. Moreover,because only the periphery of material 58 was clamped during the formingprocess and need be trimmed, the vast remaining majority of the material58 was available to create products. The processes of the invention maybe repeated for any number of sheets of material.

Exemplary holder 70A includes six formed portions 66, five generallycircular in shape and configured to receive a coin for display (see,e.g., FIG. 7). In FIG. 6, the sixth formed portion (66A) of holder 70Aincludes embossed letters “USA.” By contrast, many of unformed portions62 include color printing, with additional text and art work 74 printedthereon. Distortion-free text spelling “TEST” in printed areas ofunformed portions 62 renders apparent the fact that the portions 62 didnot distort while portions 66 were forming. Because holder 70A is merelyone of many examples of holders capable of being made by the presentinvention, in no way is the invention limited to holders having anyparticular number or type of formed portions 66 or unformed portions 62.(Further, although not presently preferred, any of portions 66 mayinclude distorted printing that becomes more legible when portions 66are formed.)

Because plugs 30 may include notches 35 against which material 58 may befashioned, formed portions 66 may include a corresponding number of“crush tabs” or “click-in features” protruding inward into thecoin-receiving regions. These tabs provide some tolerances for portions66. If, for example, a portion 66 is slightly larger in diameter than ato-be-received coin, the coin, when inserted, may (frictionally) bearagainst the inwardly-protruding tabs to be retained in position. Ifunneeded, the tabs will be crushed or otherwise deformed upon insertionof the coin so as not to impede its retention.

The foregoing is provided for purposes of illustrating, explaining, anddescribing embodiments of the present invention. Modifications andadaptations to these embodiments will be apparent to those skilled inthe art and may be made without departing from the scope or spirit ofthe invention.

1. Apparatus for thermoforming a plastic material, comprising: a. amold; b. means for positioning a plastic material adjacent the mold, theplastic material defining integral first and second regions; and c.means for selectively heating the first region to its formingtemperature while maintaining the second region at less than its formingtemperature when the plastic material is positioned adjacent the mold.2. Apparatus according to claim 1 in which the mold is configured to beevacuated and the selective heating means is configured so as tothermoform the first region but not thermoform the second regionfollowing evacuation of the mold.
 3. Apparatus according to claim 2 inwhich the selective heating means includes: a. a source of energy; andb. an energy sink.
 4. Apparatus according to claim 3 in which the heatsink has a depth and at least one cut-out extending through the depth.5. Apparatus according to claim 4 in which the mold defines an uppersurface and comprises at least one plug protruding therefrom. 6.Apparatus according to claim 5 in which the heat sink is configured sothat the at least one cut-out may be aligned with the at least one plug.7. Apparatus according to claim 6 further comprising the plasticmaterial positioned between the heat sink and the upper surface of themold. 8-16. (canceled)
 17. Apparatus according to claim 5 in which theplug is generally cylindrical in shape with at least one circumferentialnotch.